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01.12.2014 | Research article | Ausgabe 1/2014 Open Access

The Journal of Headache and Pain 1/2014

Expression of 5-HT3 receptors and TTX resistant sodium channels (NaV1.8) on muscle nerve fibers in pain-free humans and patients with chronic myofascial temporomandibular disorders

Zeitschrift:
The Journal of Headache and Pain > Ausgabe 1/2014
Autoren:
Nikolaos Christidis, Isabell Kang, Brian E Cairns, Ujendra Kumar, Xudong Dong, Annika Rosén, Sigvard Kopp, Malin Ernberg
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​1129-2377-15-63) contains supplementary material, which is available to authorized users.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

NC, contributed in the design of the study, by collecting the material (microbiopsies), in the statistical analysis, and as the main author of the manuscript. IK contributed in the analysis of the material and in the result section of the manuscript. BEC, contributed in the design of the study, in the analysis of the material, in the statistical analysis, and in the manuscript in general. UK, contributed in the analysis of the material and in the discussion section of the manuscript. XD, contributed in the analysis of the material and in the discussion section of the manuscript. AR, contributed by collecting the material (traditional biopsies) and in the discussion section of the manuscript. SK, contributed in the design of the study and in the result and discussion section of the manuscript. ME, contributed in the design of the study, in the statistical analysis, and in the manuscript in general. All authors read and approved the final manuscript.

Abstract

Background

Previous studies have shown that 5-HT3-antagonists reduce muscle pain, but there are no studies that have investigated the expression of 5-HT3-receptors in human muscles. Also, tetrodotoxin resistant voltage gated sodium-channels (NaV) are involved in peripheral sensitization and found in trigeminal ganglion neurons innervating the rat masseter muscle. This study aimed to investigate the frequency of nerve fibers that express 5-HT3A-receptors alone and in combination with NaV1.8 sodium-channels in human muscles and to compare it between healthy pain-free men and women, the pain-free masseter and tibialis anterior muscles, and patients with myofascial temporomandibular disorders (TMD) and pain-free controls.

Methods

Three microbiopsies were obtained from the most bulky part of the tibialis and masseter muscles of seven and six healthy men and seven and six age-matched healthy women, respectively, while traditional open biopsies were obtained from the most painful spot of the masseter of five female patients and from a similar region of the masseter muscle of five healthy, age-matched women. The biopsies were processed by routine immunohistochemical methods. The biopsy sections were incubated with monoclonal antibodies against the specific axonal marker PGP 9.5, and polyclonal antibodies against the 5-HT3A-receptors and NaV1.8 sodium-channels.

Results

A similar percentage of nerve fibers in the healthy masseter (85.2%) and tibialis (88.7%) muscles expressed 5-HT3A-receptors. The expression of NaV1.8 by 5-HT3A positive nerve fibers associated with connective tissue was significantly higher than nerve fibers associated with myocytes (P < .001). In the patients, significantly more fibers per section were found with an average of 3.8 ± 3 fibers per section in the masseter muscle compared to 2.7 ± 0.2 in the healthy controls (P = .024). Further, the frequency of nerve fibers that co-expressed NaV1.8 and 5-HT3A receptors was significantly higher in patients (42.6%) compared to healthy controls (12.0%) (P < .001).

Conclusions

This study showed that the 5-HT3A-receptor is highly expressed in human masseter and tibialis muscles and that there are more nerve fibers that express 5-HT3A-receptors in the masseter of women with myofascial TMD compared to healthy women. These findings indicate that 5-HT3-receptors might be up-regulated in myofascial TMD and could serve as potential biomarkers of chronic muscle pain.
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